Active efforts have been made in these years for the development of so-called polymer batteries which use electroconductive organic polymers such as polyaniline, polypyrrole, and polyacetylene as the electrode material. Among others, nonaqueous electrolyte secondary cells using polyaniline in the positive electrode have advantages of a high voltage and improved shelf storage. They are expected to find commercial applications as a memory backup power supply for computers and as a power supply for portable equipment. In fact, some polyaniline batteries are on the verge of entering commercial manufacture.
In the applications as a memory backup power supply for computers and as a power supply for portable equipment, the circuitry often causes the cells to be discharged beyond the rated capacity. That is, the cells are often operated in a over-discharge state for a prolonged period of time. Under the over-discharge conditions, lead acid batteries undergo irreversible reaction of electrode active materials, eventually resulting in a partial or sometimes complete loss of cell performance. In extreme cases, leakage of the electrolytic solution can occur, causing a failure of the circuitry itself. For nonaqueous electrolyte secondary cells using metal oxides such as manganese dioxide and vanadium pentoxide and chalcogenides such as molybdenum sulfide as the positive electrode, it is also known that the positive electrode active material is damaged by over-discharge to such an extent that normal charging/discharging operation is no longer possible. As to the nonaqueous electrolyte secondary cells using a conductive organic polymer, typically polyaniline as the positive electrode active material, there are available at present no cells which show satisfactory over-voltage recovery.